Need help with postgresql build on windows

Hi,

On Mon, 5 Jan 2026 at 08:28, Prafulla Ranadive
<pprandive.pgsql@gmail.com> wrote:

Hello,

I have started exploring Postgresql recently.
I am trying to build Postgresql from source on a windows machine. I am

referring to the page
https://www.postgresql.org/docs/current/install-meson.html#INSTALL-SHORT-MESON

The ninja command is failing with the error message:

PS C:\PostgreSQLworkspace\postgres\build> ninja
[142/2102] Generating src/fe_utils/psqlscan with a custom command
FAILED: src/fe_utils/psqlscan.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir" "src/fe_utils/psqlscan.c.p"
"--flex" "C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i" "../src/fe_utils/psqlscan.l" "-o"
"src/fe_utils/psqlscan.c" "--no-backup" "--" "-Cfe" "-p" "-p"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\fe_utils\psqlscan.c

[146/2102] Generating src/backend/bootstrap/bootscanner with a custom

command

FAILED: src/backend/bootstrap/bootscanner.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir"
"src/backend/bootstrap/bootscanner.c.p" "--flex"
"C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i"
"../src/backend/bootstrap/bootscanner.l" "-o"
"src/backend/bootstrap/bootscanner.c"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\backend\bootstrap\bootscanner.c

[147/2102] Generating src/backend/parser/scan with a custom command
FAILED: src/backend/parser/scan.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir"
"src/backend/parser/scan.c.p" "--flex"
"C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i" "../src/backend/parser/scan.l" "-o"
"src/backend/parser/scan.c" "--no-backup" "--" "-CF" "-p" "-p"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\backend\parser\scan.c

ninja: build stopped: subcommand failed.
PS C:\PostgreSQLworkspace\postgres\build>

I have enabled full permission on the folder but still no luck.

Can someone please help me with this? Any troubleshooting pointers would

be a great help!

Could you let me know where you downloaded flex from? I am wondering
whether it might be this:
https://gnuwin32.sourceforge.net/packages/flex.htm.

For our Windows CI, we use flex and bison from this release instead:
https://github.com/lexxmark/winflexbison/releases/tag/v2.5.24.

If you have a chance, would you mind trying flex and bison from that
source to see if it helps?

--
Regards,
Nazir Bilal Yavuz
Microsoft

Hi Nazir,

Thank you for your email. Sure, I will try using flex bison from link
shared by you.
I have stepped out for some personal work so I will be able to try out
only after 4 hours from now.
I will let you know as soon as I try that out. Once again thank you so
much.

Regards,
Prafulla

On Mon, 5 Jan, 2026, 12:09 pm Nazir Bilal Yavuz, <byavuz81@gmail.com>
wrote:

Hi,

On Mon, 5 Jan 2026 at 08:28, Prafulla Ranadive
<pprandive.pgsql@gmail.com> wrote:

Hello,

I have started exploring Postgresql recently.
I am trying to build Postgresql from source on a windows machine. I am

referring to the page
https://www.postgresql.org/docs/current/install-meson.html#INSTALL-SHORT-MESON

The ninja command is failing with the error message:

PS C:\PostgreSQLworkspace\postgres\build> ninja
[142/2102] Generating src/fe_utils/psqlscan with a custom command
FAILED: src/fe_utils/psqlscan.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir" "src/fe_utils/psqlscan.c.p"
"--flex" "C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i" "../src/fe_utils/psqlscan.l" "-o"
"src/fe_utils/psqlscan.c" "--no-backup" "--" "-Cfe" "-p" "-p"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\fe_utils\psqlscan.c

[146/2102] Generating src/backend/bootstrap/bootscanner with a custom

command

FAILED: src/backend/bootstrap/bootscanner.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir"
"src/backend/bootstrap/bootscanner.c.p" "--flex"
"C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i"
"../src/backend/bootstrap/bootscanner.l" "-o"
"src/backend/bootstrap/bootscanner.c"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\backend\bootstrap\bootscanner.c

[147/2102] Generating src/backend/parser/scan with a custom command
FAILED: src/backend/parser/scan.c
"C:\MyPrograms\Meson\meson.exe" "runpython" "../src/tools/pgflex"

"--builddir" "." "--srcdir" ".." "--privatedir"
"src/backend/parser/scan.c.p" "--flex"
"C:\MyPrograms\GnuWin32\bin\flex.EXE" "--perl"
"C:\Strawberry\perl\bin\perl.EXE" "-i" "../src/backend/parser/scan.l" "-o"
"src/backend/parser/scan.c" "--no-backup" "--" "-CF" "-p" "-p"

C:\MyPrograms\GnuWin32\bin\flex.EXE: can't open

C:\PostgreSQLworkspace\postgres\build\src\backend\parser\scan.c

ninja: build stopped: subcommand failed.
PS C:\PostgreSQLworkspace\postgres\build>

I have enabled full permission on the folder but still no luck.

Can someone please help me with this? Any troubleshooting pointers

would be a great help!

Could you let me know where you downloaded flex from? I am wondering
whether it might be this:
https://gnuwin32.sourceforge.net/packages/flex.htm.

For our Windows CI, we use flex and bison from this release instead:
https://github.com/lexxmark/winflexbison/releases/tag/v2.5.24.

If you have a chance, would you mind trying flex and bison from that
source to see if it helps?

--
Regards,
Nazir Bilal Yavuz
Microsoft